The human body functions through a number of interdependent physiological systems controlled through various mechanical, electrical, and chemical processes. The metabolic state of the body is constantly changing. For example, as exercise level increases, the body consumes more oxygen and gives off more carbon dioxide. The cardiac and pulmonary systems maintain appropriate blood gas levels by making adjustments that bring more oxygen into the system and dispel more carbon dioxide. The cardiovascular system transports blood gases to and from the body tissues. The respiratory system, through the breathing mechanism, performs the function of exchanging these gases with the external environment. Together, the cardiac and respiratory systems form a larger anatomical and functional unit denoted the cardiopulmonary system.
Various disorders that affect the cardiovascular system may also impact respiration. For example, heart failure is an abnormality of cardiac function that causes cardiac output to fall below a level adequate to meet the metabolic demand of peripheral tissues. Heart failure is usually referred to as congestive heart failure (CHF) due to the accompanying venous and pulmonary congestion. Congestive heart failure may have a variety of underlying causes, including ischemic heart disease (coronary artery disease), hypertension (high blood pressure), and diabetes, among others.
Various types of disordered respiration are associated with CHF. Respiration rate is linked to the patient's physical condition and is indicative of the patient's disease or health state. In some types of chronic diseases, changes in respiratory rate are gradual over time and may be measured over months or years. However, in heart failure decompensation, increases in respiratory rate can occur over hours or days. Clinical data collected in the ambulatory setting has demonstrated a statistically significant difference between respiration rate distributions from healthy subjects as compared to HF patients. Moreover, there is a statistically significant difference in the pattern for stable HF patients as compared to decompensated HF patients.
Rapid shallow breathing is one of the cardinal signs of heart failure. When the patient at rest spends more time at higher respiration rates, this is indicative of a worsening of their HF status. The appearance of rapid, shallow breathing in a CHF patient is often secondary to increased pulmonary edema, and can indicate a worsening of patient status. An abnormally high respiration rate thus can be an indicator of CHF decompensation.
Symptoms of dyspnea are among the primary reasons that reduce patients' quality of life and are a primary reason why many HF patients return to the hospital during a HF decompensation episode. It is estimated that nearly one million hospital admissions for acute decompensated congestive heart failure (CHF) occur in the United States each year, which is almost double the number admitted 15 years ago. The re-hospitalization rates during the 6 months following discharge are as much at 50%. Nearly 2% of all hospital admissions in the United States are for decompensated CHF patients, and heart failure is the most frequent cause of hospitalization in patients older than 65 years. The average duration of hospitalization is about 6 days. Despite aggressive therapies, hospital admissions for CHF continue to increase, reflecting the prevalence of this malady.
Because of the complex interactions between the cardiovascular, pulmonary, and other physiological systems, as well as the need for early detection of various diseases and disorders, an effective approach to monitoring and early diagnosis is needed. Accurately characterizing patient respiration aids in monitoring and diagnosing respiration-related diseases or disorders. Evaluating patient respiration information may allow an early intervention, preventing serious decompensation and hospitalization.